Catch up on the timeline and key developments in this story before the hearing. Politico has provided such a handy tool, here.

There are numerous implications when it comes to the possible collusion with Russia.

Related: Heinrich responds to Comey firing and Trump

In May, when Comey was let go, Chris Matthews of MSNBC’s Hardball spoke with Senator Heinrich to get his reaction to the firing:

There are a lot of things to be unsure of right now. The current administration has stirred the pot of what Americans knew to be – and now we are wondering what the future holds for: education, healthcare, marriage equality and equal rights.